I am trying to find an example that will demonstrate the difference between
$PrePrint and $Post. I found an old thread in this news group where a
user wanted to display all matrices using MatrixForm. Some users suggested
the following:
In[1]:= $Post=(#/.mtrx_?MatrixQ:>MatrixForm[mtrx]&);
Then Dave Withoff said it's better to assign this to $PrePrint since the
objective here is to adjust the display rather than the result of the
calculation. With the assignment to $Post you could, for example, get
unexpected results from calculations using %, since matrices will be wrapped
in MatrixForm.
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However, if we use $Post above, the next input will compute the inverse
the matrix. I did verify that Inverse can't take a matrix wrapped in
MatrixForm. Can somebody give an example where doing this with $PrePrint
instead of $Post gives a different result.
In[2]:= m={{2,3},{0,1}};
Inverse[%]
Out[3]= (* Inverse of (m) in MatrixForm, not shown. *)
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Thanks,
Ted Ersek
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